Milestone is developing a followup in Japan, which contains everything the first disc offered, plus two more games. Milestone Shooting Collection 2 includes all three of the aforementioned games, plus Radio Allergy Noir (a version of which was released as a standalone, full-price Xbox 360 game) and Illvelo, which was once planned for North American release but canceled. Perhaps North American publisher UFO Interactive will give Illvelo a second chance by bringing this collection over. If you want the import, it's out in Japan on December 30.
You can see more of each game at the official site.